Risk factors for breast cancer among women in Ekurhuleni Metropolitan Municipality, Gauteng Province of South Africa, 2017–2020: a case-control study

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Background: Breast cancer (BC) is the most common cancer among women in South Africa (SA). In 2020, the age-standardized incidence rate (ASIR) and the age-standardized mortality rate (ASMR) were 52.6 and 16.0 per 100 000, respectively. There is a paucity of evidence on the risk factors for BC among women of all population groups in SA. The goal of this study was to determine the risk factors for BC, calculate the ASIR as well as explore epidemiological changes in BC among women in Ekurhuleni Metropolitan Municipality, Gauteng Province, SA. Methods: An unmatched case-control study was conducted from 1 January 2017 to 31 December 2020 using secondary data extracted from the Ekurhuleni Population-Based Cancer Registry (EPBCR). Unconditional multivariable logistic regression analysis was carried out using the adjusted odds ratio (aOR). The variables race, employment, HIV, smoking and alcohol statuses were included in the multivariable logistic regression model while the model was adjusted for age. In addition to risk factor analyses, we calculated the ASIR for BC in women using the Statistics South Africa population estimates as a denominator and the Segi-World Standard Population (WSP) for standardization. The joinpoint regression program was used to estimate the average annual per cent change (AAPC) for the four years (2017–2020). Results: A total of 3068 (2217 cases and 851 controls) participants were enrolled in the study. The mean age (±SD) in years of the participants was 55.2 (±15.2). The White population group, being self-employed and Human Immunodeficiency Virus (HIV) -positive status was significantly associated with reduced odds of BC development among women. Women who were HIV-positive were 61% less likely to have BC than women who were HIV-negative (aOR 0.39; 95%CI: 0.27‒ 0.57). White women were 75% less likely to have BC than women of other races (aOR 0.35; 95%CI: 0.29‒0.43). Self-employed women were 59% less likely to have BC than women who v were formally employed (aOR 0.41; 95%CI: 0.18‒0.97). The ASIR for BC among all women in 2017 was 42.33 (95%CI: 39.25–45.59) and 23.39 (95%CI: 21.10–25.86) per 100 000 in 2020. White women had the highest incidence rate of BC throughout the study period (55.47 (95%CI: 47.57–65.08) in 2017, 69.70 (95%CI: 60.77–79.74) in 2018, 35.51 (95%CI: 29.29–42.85) in 2019 and 37.12 (95%CI: 30.74–44.62) in 2020) compared to other population groups. No significant reduction in BC incidence rate was observed among all women throughout the study period with an exception of Black women, whereby a significant reduction in BC incidence rate was observed between 2017 and 2020 with an AAPC of -23.5% (p=0.017) Conclusion: In this study, the White population group, being self-employed and HIV-positive had lower odds of BC and thus necessitate more in-depth studies using primary data to effectively explore the risk factors of BC among women in SA settings. There was no significant change in AAPC except for Black women, this indicates disparities in screening uptake among population groups, and as such, there is a need to strengthen BC preventive strategies. There is a need for public health awareness to scale up BC screening uptake as well as the promotion of early detection through targeted awareness campaigns.
A research report submitted in partial fulfilment of the requirement for the degree of Master of Science in Epidemiology to the Faculty of Health Sciences, University of the Witwatersrand, School of Public Health, Johannesburg, 2023
Incidence, Risk factor, Breast cancer, Ekurhuleni Metropolitan Municipality